Benchmark
A frozen reference figure that later results are measured against.
A benchmark is a number you record before you change anything, so that afterwards you can tell whether the change did something. Your median views over the last twenty posts. Your typical engagement per view. Your usual watch-through on a given format.
The word "frozen" is doing the work. A benchmark that updates as new results arrive will quietly absorb whatever you just did, and the comparison becomes circular: you end up measuring your new content against itself. Take the snapshot, write it down, leave it alone.
Medians beat averages here. One runaway post drags an average far enough to make an ordinary month look exceptional, which is exactly the error a benchmark exists to prevent.
Where this comes up
One variable, a frozen benchmark, a sample size decided in advance, and a result you agreed to accept before you saw it.
The difference between a number a system counted and a number someone told you, and why almost every content report quietly mixes the two together.